The invention relates to new azo dyes, a process for their preparation, and their use for dyeing or printing materials, in particular organic or fiber-containing materials, to produce materials with brownish shades.
In order to produce papers with a brown shade, it is known to dye paper with mixtures of different dyes. For example, WO-A 2007/057370 is directed to liquid formulations containing the direct dyes C.I. Direct Brown 44 and Direct Yellow 11. EP-A-1 258 562 relates to dye mixtures containing two anionic dyes each with a different, defined absorption maximum. WO-A 2004/048478 teaches the production of a low-salt liquid formulation of C.I. Direct Brown 44. The production process comprises production of vesuvine from m-phenylenediamine and direct conversion to C.I. Direct Brown 44. Vesuvine and its coupling products, such as C.I. Direct Brown 44, have been known since the beginning of dye chemistry. For instance, the Colour Index (C.I.) shows that C.I. Direct Brown 44 is obtained by formally coupling two parts of sulfanilic acid onto one part of vesuvine (Bismarck Brown C.I. 21000). However, the lightfastness of the produced brown papers is often not sufficient. From JP 2001-004833 A1 there is known a polarizing film for liquid crystal projector including an azo compound of specified structure which contains at least two azo groups linked by three aromatic groups.
In paper mills or paper processing industry, brownish papers often are stored without being prevented from the influence of light or weather, which results in change of color or color shade. Therefore, there is a need for improving the lightfastness of brownish papers.
Surprisingly, it has been found that this problem can be solved by new azo dyes containing at least three azo groups which are linked by aromatic structures, such as substituted benzene and/or naphthalene groups. These azo dyes are soluble in water and enable the production of materials, in particular of organic or fiber-containing materials, e.g. paper or board, in brownish shades and with high lightfastness. In particular, it was surprising that the brownish shade could be obtained with the use of one dye only, in contrast to the prior art, which commonly uses dye mixtures for that purpose.
Thus, the present invention provides compounds of the general formula (1)
                A represents        
                and B represents        
or
A, B independently of each other, represent one of the following groups:
wherein    R1, R2, R3, R4 independently of each other, represent hydrogen, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1-C4 alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted phenyl, amino, sulfonic, carboxyl, hydroxyl, nitro, or halogen groups.
Surprisingly, it was found that compounds of formula (1) are soluble in water, and materials dyed with those dyes show improved lightfastness.
The invention also refers to a process for preparing the compounds of formula (1), comprising diazotizing a compound of formula (2) or formula (2a)
coupling the obtained product with a compound of formula (3)
diazotizing the obtained product and coupling with a compound of formula (4)
diazotizing the obtained product and coupling with a compound of formula (5) or formula (5a)
to obtain the compound of formula (1).
Further, the invention refers to the use of the compounds of formula (1) for dyeing or printing materials, in particular materials containing cellulose and/or polyamide, preferably paper or board. In addition, the invention relates to a process for dyeing or printing materials, in particular materials containing cellulose and/or polyamide, preferably paper or board, and to materials or paper obtained by that process. Preferred embodiments of the invention are described in the description hereinafter and the claims. In the present invention, the term paper is used to cover paper or board.